The transtheoretical model (TTM; Prochaska, DiClemente, & Norcross, 1992) suggests that, at any point, an individual is in one of five stages-of-change related to adopting a behavior. People sequentially advance in stage but may also maintain or even regress, based on personal and environmental factors (Nigg, 2005). A classic study published in this journal in 1992 (Marcus, Selby, Niaura, & Rossi, 1992) indicated that as TTM stages advance, exercise barriers self-efficacy (i.e., self-regulatory efficacy) increases. Research on adults (Carron, Hausenblas, & Estabrooks, 2002) has consistently supported this finding, but it has not been well studied in children. The intent of this present investigation was threefold: (a) to further assess reliability of the Exercise Barriers Self-Efficacy Scale for Children (EBSES-C) in a sample of African American preadolescents; (b) to replicate and extend the research on adults, suggesting that as the TTM stage is more advanced, self-regulatory efficacy is greater (Marcus et al., 1992); and (c) to examine possibilities of change in exercise barriers self-efficacy significantly mediating the relationship between changes in TTM stage and voluntary physical activity in response to a behavioral treatment. (Contains 2 tables.)